Hi,

I've bought a max/min multimeter as recommended by you all.

The voltage before I started the car was 12.2V

When I started the car the voltage dropped to 9.1V minimum during
staring.

Once the engine was running, the voltage was 14.5V maximum.

Am I right to be worried about the 9 volts? It seems low to me but
OTOH I am not having any problems starting the car at the moment, so
isn't that the biggest test of the battery?

I compared it to my other half's car and the voltages for that we
12.4V before, 10.1V during, and 14.6V after starting.

By the way, the multimeter claims to have two settings to test 1.5V
and 9V batteries. The manual claims it puts a small load across the
battery and displays the voltage. Anything about 1.2V is ok for a 1.5V
battery, and anything over 7.2V is ok for a 9v battery, or so it says.
I had some flat 1.5V batteries that measured 1.25v, so they passed the
meter test but were useless in practical terms. Are these [non-car]
battery test settings a waste of time? I seem to remember that when I
was at school we were told you should test a battery by its current,
not its voltage?

TIA

On Sat, 30 Jan 2010 09:17:48 -0000, Fred
wrote:

Hi,

I've bought a max/min multimeter as recommended by you all.

The voltage before I started the car was 12.2V

When I started the car the voltage dropped to 9.1V minimum during
staring.

Once the engine was running, the voltage was 14.5V maximum.

Am I right to be worried about the 9 volts? It seems low to me but
OTOH I am not having any problems starting the car at the moment, so
isn't that the biggest test of the battery?


That's the critical bit, the 9V just tells you that it's borderline, the
14.5V tells you the alternators working properly

I compared it to my other half's car and the voltages for that we
12.4V before, 10.1V during, and 14.6V after starting.

By the way, the multimeter claims to have two settings to test 1.5V
and 9V batteries. The manual claims it puts a small load across the
battery and displays the voltage. Anything about 1.2V is ok for a 1.5V
battery, and anything over 7.2V is ok for a 9v battery, or so it says.
I had some flat 1.5V batteries that measured 1.25v, so they passed the
meter test but were useless in practical terms. Are these [non-car]
battery test settings a waste of time? I seem to remember that when I
was at school we were told you should test a battery by its current,
not its voltage?

TIA

Generally they'll just tell you when it's dead flat.

"Fred" wrote in message
...
Hi,

I've bought a max/min multimeter as recommended by you all.

The voltage before I started the car was 12.2V

If meter is accurate, and battery fully charged and healthy you should be
seeing 12.5 - 6v at rest.

dropping to 9v under cranking is somewhat low. I would say you have a dead
cell.

Tim..

In article ,
Fred wrote:
I've bought a max/min multimeter as recommended by you all.

The voltage before I started the car was 12.2V

Battery not fully charged - but not uncommon in practice. Or it could be
on the way out. Only way to be sure is a proper test with an electronic
tester. Your local battery specialist will have one as do Halfords. But of
course you have to trust the operator. ;-)

When I started the car the voltage dropped to 9.1V minimum during
staring.

That is distinctly borderline. Could indicate the battery is past its best
or the starter motor taking too much current. The first is far more
likely.

Once the engine was running, the voltage was 14.5V maximum.

Again suggesting a low battery. It should be approx 13.8 when fully
charged. Either charge the battery externally or check again after a
daylight run of about 20 miles.

--
*If God dropped acid, would he see people?

Dave Plowman London SW
To e-mail, change noise into sound.